The present invention relates to a device for optimising mixing and distribution of two fluids constituted, for example, by an essentially gaseous phase usually at least partially comprising hydrogen and a liquid phase essentially composed of hydrocarbons, said device being located upstream of a granular bed or between two granular beds comprising solid particles, the granular solids advantageously possessing catalytic activity. Such mixing and distribution systems are generally integrated into a fixed bed reactor in which the fluid flow is in co-current dropper mode through said solid bed or beds of granular solid.
The present description will refer equally both to injection, mixing and distribution systems and to devices.
Such systems can generally be located upstream of a granular bed, more particularly at the head of a reactor.
In particular, the present invention is applicable in all cases:
where gas phases are in the majority with respect to the liquid phases, i.e., where the volume ratio between the gas and liquids is usually more than 3:1 and normally less than 400:1 (3 less than gas volume/liquid volume less than 400);
where the gas phases are in the minority with respect to the liquid phases, i.e., where the volume ratio between the gas and liquids is usually more than 0.1:1 and normally less than 1:1 (0.1 less than gas volume/liquid volume less than 1);
where the reaction is highly exothermic and requires the introduction of a supplementary fluid into the reactor, usually a gas, to cool the gas/liquid mixture;
where the reaction necessitates close contact to dissolve a compound that is usually gaseous (for example hydrogen H2) in the liquid phase.
The present invention is of particular application to gas/liquid distributors such as those used to implement hydrocracking, hydrotreatment, hydrodesulphurisation, hydrodenitrogenation, selective or complete hydrogenation of C2 to C5 cuts, selective hydrogenation of steam cracked gasoline, hydrogenation of aromatic compounds in aliphatic and/or naphthenic cuts, and hydrogenation of olefins in aromatic cuts.
It is also of application to carrying out other reactions requiring good mixing of a gas phase with a liquid phase, for example partial or complete oxidation reactions, amination, acetyloxidation, ammoxidation and halogenation reactions, in particular chlorination.
In the specific field of hydrodesulphurisation, hydrodenitrogenation and hydrocracking reactions to produce high conversions (to obtain a product containing, for example, 30 ppm (parts per million) of sulphur or less), the distribution of both gas and liquid must be good, but principally the liquid distribution must be good, as the volume ratios are generally between about 3:1 and about 400:1, usually between about 10:1 and about 200:1; and when using a quench, very good contact between the introduced gas cools the process fluids.
In order to optimise the distribution of a fluid compound, in general at least one gas phase and at least one liquid phase, one solution proposed in the prior art consists of mixed injection gas/liquid distribution systems for dropper flows.
French patent FR-A-2 745 202 and U.S. Pat. No. 5,688,445 propose a plate with conduits provided with holes staged along the conduit for the passage of gas (upper holes) and liquid (lower holes). No system was envisaged in that prior art to prevent fluctuations in the liquid/gas interface above the plate due to injection of liquid into the head of the reactor. Because of their configuration, an imbalance in this interface causes an imbalance in the gas and liquid flows from one conduit to another.
International patent WO-A-95/35159 proposes a two-level distribution system; the second level is constituted by a plate with conduits pierced with holes in their portion located above a plate and in their portion located below the plate. The disadvantage of the plate lies in the fact that the flexibility in the liquid flow rate is obtained by employing two types of conduits. The liquid flow rate, therefore, determines the density of the injection points. Further, using two levels takes up a great deal of space in the reactor head.
U.S. Pat. No. 4,140,625 proposes a plate system traversed by venturi tubes. The gas is injected into the head of the venturi tubes and liquid is injected at the neck or upstream of the constriction. The gas/liquid mixture is then injected into the catalytic bed. The disadvantage of that system is that its flexibility is low regarding the liquid flow rate since there is only one level for the holes for the liquid.
In summary, it can be concluded that of the systems proposed in those different patents using a liquid and gas phase mixed injection plate:
either the plate offers considerable flexibility as regards liquid flow rate but does not possess any means for stabilising the gas/liquid interface upstream of the plate;
or the plate has two levels to amortise fluctuations in the gas/liquid interface but only has a little flexibility as regards the liquid flow rate.
In contrast to the present invention, in dropper mode gas/liquid injection systems, prior art systems are exclusively supplied by a gas/liquid flow at the reactor inlet. The system of the invention presents an alternative and innovative solution to the problems encountered with prior art devices. The flexibility of the present invention is high as regards the liquid flow rate, and fluctuations in the gas/liquid interface are absent.
The present invention provides a device for producing a polyphase mixture of two fluids and their distribution comprising a chamber for the passage of a first fluid, said chamber being pierced by perforated tubes or conduits forming a passage through the chamber for a second fluid in a physical state that is different from the first fluid or which is not miscible with the first fluid, said tubes being pierced by at least one orifice allowing the passage of the first fluid and mixing of the two fluids via the tubes, said second fluid being injected upstream of said device and the first fluid being injected into said device.
In general, the first fluid is essentially liquid and the second fluid is essentially gaseous. In a further implementation, the first fluid is essentially liquid and the second fluid is essentially a second liquid that is not miscible with the first fluid.
Advantageously, the device is located close to the reactor head.
Preferably, said chamber is supplied with the first fluid by injection thereof in a direction laterally to said device at at least one point.
In general, the second fluid is injected axially downstream of said device.
In a particular implementation, the tubes extend a distance ht below the chamber.
The invention also concerns a reactor of elongate form along one axis, comprising at least one device in accordance with the invention for mixing and distributing two fluids in different physical states, comprising at least one bed of granular solids downstream of at least one mixing and distributing device, and two separate lines for injecting fluids into said device, said first fluid being injected into said device, normally substantially perpendicularly with respect to the axis of the reactor and injection of the second fluid into said device being carried out upstream of said device, normally substantially along the axial direction of the reactor.
In a preferred implementation, the liquid and gas phases circulate in a co-current dropper mode through said bed or beds of granular solids.
More particularly, the liquid feed and gas phase can be injected upstream of said bed or beds of granular solids.
Advantageously, said bed or beds of granular solids comprise at least one catalytic granular solid.
In one implementation, the first fluid is a liquid phase and the second fluid is a gas phase.
Advantageously, upstream of the reactor head, a buffer drum is provided outside the reactor connected with the device via lines to allow material exchange between the liquid phase and the gas phase, said lines allowing separate injection into the mixing device respectively of an essentially liquid phase containing dissolved gas and of an essentially gaseous phase containing liquid, said essentially liquid and essential gaseous phases resulting from prior contact of the liquid and gas phases in said buffer drum.
The device and/or reactor described in the present invention can in particular be used in hydrodesulphurisation, selective hydrogenation or hydrodenitrogenation processes.
The term xe2x80x9cessentially gaseousxe2x80x9d means a phase containing at least 50% gas, preferably at least 70% gas and more preferably at least 90% gas. The term xe2x80x9cessentially liquidxe2x80x9d means a phase containing at least 50% liquid, preferably at least 70% liquid and more preferably at least 90% liquid.
Other advantages and characteristics of the invention will become clear from the description below given by way of example.